1. Field
This disclosure relates to routing path setting in a computer network, and more particularly, to a method and a system for setting a routing path in consideration of hidden node and carrier sense interference awareness in order to improve network performance in a multi-hop wireless network, and a recording medium thereof.
2. Description of the Related Art
In a wireless mesh network which is a kind of multi-hop wireless network, network performance degrades dramatically as the size of the network increases due to the carrier sense interference and hidden node problem.
Employing multi-channel multi-radio has been shown as an effective approach to increase the wireless mesh network capacity. However, in order to obtain the maximum utilization of multi-channel networks, channels need to be assigned to links of each node so as to reduce the carrier sense interference and hidden node problem. Since the complexity of channel assignment was proven to be an NP-hard problem, a routing metric can be used to choose routing paths in a combination that considers factors such as channel diversity, intra-flow interference, inter-flow interference, and the hidden node problem after the channels are established.
The early routing metrics used for setting a routing path simply relied on hop count. However, since the hop count simply prefers only the shortest path, it is not an effective routing metric. Metric is a value, which a routing protocol consults to select an optimal path, and different metrics are used for different routing protocols.
In order to solve this problem, there was proposed an expected transmission count (ETX) metric, described in De Couto et al. D. De Couto, D. Aguayo, J. Bicket, and R. Morris, “High-throughput Path Metric for Multi-Hop Wireless Routing”, ACM MOBICOM, on September 2003. The ETX estimates the status of the link by using the link packet loss ratio as a base for choosing a path with the best link quality. However, although it shows better performance than the shortest path, link bandwidth of the links was not considered, and only the link packet loss ratio was considered. In addition, a path with high channel diversity could not be selected, and the hidden node problem could not be solved.
In order to solve the problems of the ETX, there was disclosed a system and a method for link quality routing using a weighted cumulative expected transmission time metric in Korean Patent Publication No. 10-2006-0092811 filed on Jun. 22, 2005, by R. Draves, J. Padhye, and B. Zill. This method came to solve the channel diversity problem in the ETX. Furthermore, this method proposed an expected transmission time (EU) by improving the ETX using link bandwidth. Since each individual link uses ETX value, the EU calculates a time needed to transmit a single packet including retransmission over a link. A path is selected by calculating the total delay of a packet on the basis of those values and incorporating channel diversity.
Although the WCETT solves some of the problems in the ETX, it still has some problems.
The first problem is that the WCETT cannot distinguish or avoid a hidden node path since it does not consider hidden the node problem just like the ETX.
The second problem is that although links using the same channel on a path interfere with each other only in the case where they are in the carrier sense range, the WCETT includes links using the same channel for estimating the bottleneck channel over that path regardless of their location in the path, so that accurate calculation is impossible.
The third problem is that the WCETT did not consider the inter-flow interference but considered only the intra-flow interference.
To solve the hidden node problem that was not solved by the WCETT and the ETX, there was proposed “Hidden node problem aware routing metric for wireless LAN mesh networks,” (IEEE PIMRC 2007) by J. Sangiamwong, T. Sugiyama. A routing metric distinguishes a hidden node by exchanging local link state announcement packets broadcasted in a neighbor discovery step in IEEE 802.11s and calculates a packet collision ratio due to the hidden node problem in consideration of packet transmission time in a MAC layer so as to be used for path selection. However, the routing metric could not suitably estimate the hidden node effect and did not consider the intra-flow or inter-flow interference.